| Peatlands are widely distributed in Alaska and contain valuable archives of past environmental variability. In the past few decades, a range of proxies has been used to infer past changes in surface-moisture conditions from oligotrophic peat stratigraphy, including testate amoebae and the stable isotope composition of peat-forming vegetation. However, calibration and validation of surface-moisture proxies in different regions and peatland types is critical to successful application and interpretation. In this study, testate amoebae, the delta13C composition of Sphagnum, and environmental conditions (e.g., pH, water-table depth) were examined at 126 sites within 12 peatlands in south-central Alaska to assess the potential of testate amoebae and delta13C as surface-moisture proxies in the region.;Results indicated that water-table depth and pH were both strongly correlated with testate amoeba community composition, consistent with previous studies. However, the relative importance of these two environmental variables varied along the sampled gradient in moisture, with pH more important in wetter habitats and water-table depth more important in drier habitats. In contrast to testate amoebae, the delta13C of Sphagnum was found to be a relatively poor indicator of water-table depth, suggesting caution in the interpretation of downcore delta13C records. Variable carbon sources for Sphagnum photosynthesis, such as CO 2 released by methanotrophic bacteria, may explain the poor relationship between delta13C of Sphagnum and water-table depth. Cross-validation of testate amoeba transfer functions indicate that water-table depth and pH can be inferred from testate amoeba communities in Alaska with mean errors of ∼8 cm and ∼0.4 pH units, respectively. Because the optimal water-table depths for taxa in Alaska were similar to those observed in other regions of North America, the data from Alaska were combined with data from elsewhere in North America. Cross validation of transfer functions for water-table depth developed from this larger dataset (n=815) had a mean error of 8 cm. Although more work is needed before delta 13C of Sphagnum can be used as a reliable proxy of past water-table depth, the testate amoeba calibration dataset developed in this study will be widely applicable to paleoenvironmental studies of oligotrophic peatlands in Alaska. |
